When the dispenser is in the form of a liquid containing bottle, bottle caps, designed to retain an additive such as a powder or tablet or liquid and to subsequently release the additive into an attached bottle upon manipulation by a user, are known in the pharmaceutical industry and more recently in the sports drinks industry. Examples of such discharge caps are disclosed in WO98/40289, WO00/27717, WO98/00348 and WO93/14990. Many of the prior art mechanisms are cumbersome and their size can cause difficulties in the packaging, transportation and display of bottles. Their bulk may also detract from the appearance of the product which is of importance in relation to certain products such as sports drinks. Others may be complex and difficult or costly to manufacture.